1. Field of the Invention
The present invention relates to an apparatus and a method for producing woodfuel briquettes, pellets, compounds, composites, agglomerates, or granulates.
2. Description of the Background Art
Feed material for the production of woodfuel briquettes, pellets, compounds, composites, agglomerates, or granulates, is most often of free-flowing consistency. The feed material is typically conveyed to processing tools by a pressing screw, where it is processed in accordance with its intended use.
To produce simple products, for example, woodfuel briquettes or pellets, it is sufficient to compress the feed material, for example, wood (saw dust, wood fiber, wood chips), and to subsequently press it through a molding tool. The qualitative expectations from such a product are thereby relatively low. The production of high-quality granulates and agglomerates from homogeneous feed material, for example, PE granulate, requires higher constructive expenditures. After compressing, the dry feed material is thereby conveyed to an agglomerator or an extruder.
In this context, the production of composite materials, primarily of thermoplastic synthetics and wood, which are marketed, for example, as window frames, and construction and furniture parts, is an area that is becoming increasingly important. The production of these composite materials is most often done in a two-step procedure, whereby in a first step, the various components, for example, wood (saw dust, wood fiber, wood chips), synthetics and bonding agents, are mixed together and fed into an agglomerator, hot mixer, or extruder. The granulates, agglomerates, compounds, or composites thus produced serve as source material for subsequent extrusion processes.
All above-mentioned processing methods start with an intensive compression of the feed material, which causes substantial heat generation due to the high pressure and intensive frictional forces. In the processing of thermoplastic synthetics, this causes a plasticizing of the feed material, and furthermore to the forming of granulates and agglomerates.
If at the input side, thermoplastic synthetics are mixed with additional materials, for example, wood, the thermoplastic synthetics form a mushy to gooey matrix after plasticization, in which the further materials are embedded. The compounds thus produced then serve, as previously described, as source material for injection molding and extrusion apparatuses to produce construction and building materials of wood-like appearance. To improve the quality of the compounds, additives, for example, bonding agents, are frequently added to the feed material, which promote a wetting of the various components during the plasticization phase.
Quality problems with the product to be produced occur on a regular basis when water is conveyed with the feed material to the compression and processing zones. Due to the high temperatures prevalent there, water evaporates instantly and causes the formation of bubbles in the product to be produced. The resulting high pore volume contradicts the original idea of maximum compacting. Furthermore, porous intermediate products have a high abrasion tendency, which makes their further processing in subsequent processing stages questionable or even impossible.
In order to avoid problems caused by the penetration of moisture or water, it is known to dry each type of feed material in separate dedicated drying devices prior to processing. The disadvantage of this procedure is the high cost resulting from maintaining suitable drying devices and the additional expenditure of keeping the operation running.
In connection with the agglomeration of scrap plastics, a method and an apparatus is known from DE 197 06 374, whereby the heat generated during the agglomeration process is utilized to evaporate the residual water in the accumulated plastic scrap. By applying systematic loosening-up measures, the flow resistance on the input side is lowered such that the developing steam escapes from the agglomerator away from the conveying direction of the feed material. By systematically channeling the steam to an injection condenser, a transition of the steam to a liquid aggregation state is made. The condensed matter is collected in the condenser and is suctioned off with a pump.
Using this method and this apparatus, plastic scraps can be dried and agglomerated in one processing step. In connection with fine and fine-grained feed materials, however, it was found that steam escaping away from the conveying direction picks up fine particles of the feed material, which, apart from the loss of feed material, causes further complications in the subsequent processing operation.
Another conventional method and corresponding apparatus is disclosed in DE 32 10 947 A1. In this device, the feed material is compressed in a conical screw press before it is finally forced through a slot or ring constriction, where its highest compression is attained. During the initial compression, water is mostly squeezed off in the area of the pressing screw. Developing steam escapes through a perforated pipe section that is attached to the pressing screw. After condensation, the steam, together with the squeezed-off water, is removed.